Conventionally, a head-up display device (hereinafter abbreviated as HUD device) that is mounted on a mobile object and configured to display a virtual image has been known. The HUD device disclosed in Patent Literature 1 includes a light source unit, a light condensing unit, a liquid crystal element, and an enlarging light guide unit. The light condensing unit collimates an illumination light emitted from a light source unit by condensation. In the liquid crystal element, liquid crystal pixels are arranged in an opening portion, the opening portion is illuminated with the illumination light to form an image, and the display light of the image is emitted in a light flux form in the emission direction corresponding to the incident direction of the illumination light. The enlarging light guide unit guides the display light from the liquid crystal element toward the projection member so that the virtual image is enlarged.
This enlarging light guide unit has a plane mirror as an optical element having no refractive power and a concave mirror as an optical element having positive refractive power, and those optical elements are located on the optical path.
By forming an image with a liquid crystal element by illumination of collimated illumination light as in Patent Literature 1, the directivity of the display light is enhanced. For that reason, it is conceivable that the display light can reliably reach the visible region provided in the mobile object, and a luminance of the virtual image is improved.
However, there is a risk that the configuration of the head-up display device would affect the visibility of the virtual image.